1. Field of the Invention
This invention relates to a method for determining the road surface condition on the real time basis while a motor vehicle is running, and a controlling device for changing the damping force of the suspension of a motor vehicle according to the determined road surface condition.
2. Description of the Related Art
In order to automatically change the damping force of the suspension according to the road surface condition while a motor vehicle is running, it is necessary to previously determine the road surface condition. Determination of the road surface condition can be effected based on an output of a level sensor which detects the height of the vehicle body of the motor vehicle, for example.
More specifically, if a stroke by which the vehicle body moves in a vertical direction or the speed of the stroke can be continuously derived from the output of the level sensor, whether the road surface condition is a bad road or not can be determined according to the frequency at which the stroke or the speed of the stroke exceeds a predetermined value.
However, in the above road surface-condition determining method, it takes a long time to derive the above frequency and it is impossible to determine the road surface condition on the real time basis. Further, it is only possible to determine whether the road surface is a bad or not when only the above frequency is used, and it is impossible to determine various road surface conditions.
As a result, even when the damping force is changed according to the result of determination obtained by the above determining method, the damping force may not be optimum for the actual road surface condition.